Flow Field Characterization at the Onset of Gas Entrainment in a Single Downward Discharge Using Particle Image Velocimetry

Abstract

The incipience of two-phase flow in discharging branches from a stratified gas-liquid region has major implications in industrial applications where safety is of concern. An experimental investigation of the liquid side flow field at the onset of gas entrainment, in a single downward oriented discharging branch, was presented. Particle image velocimetry was used to measure the liquid side flow field in horizontal and vertical planes. Averaged velocity profiles were presented and demonstrated a highly radial flow. The particle image velocimetry data were validated using continuity and showed that the mass flow rate to be in the range of 10–25% of the expected value. Further, the vortex-free flow field assumption, used previously in the development of analytical and empirical models, was found to be reasonable.

Techniques of PIV in stratified two-phase headers

“…The design of the support structure was based on aligning the camera axes perpendicularly with the cast acrylic tube exterior surface. In their study, Bowden and Hassan [23] also aligned the single camera axis vertically, with the field of view looking down on the light sheet. With 3d-PIV the two cameras are mounted in the same plane with their CCD axes (line passing through and parallel to the CCD chip) generally aligned at 90°to each other.…”

“…The flow field is expected to be strongly dependent on the radial dimension, r, as was previously discussed by Bowden and Hassan [23]. The velocity profiles were extracted from the temporally averaged 3d vector fields by averaging the velocity at constant radial distances.…”

“…To determine the imaging planes some knowledge of the flow phenomena, as well as expectations of the desired results, was needed. In their earlier work Bowden and Hassan [23] had demonstrated, using 2d-PIV, horizontal image planes could be used to characterize the onset of gas entrainment flow field. The vertical image planes they investigated did pose an inherent problem with light reflections, on solid surfaces and the air-water interface, causing some distortion and loss of image quality.…”

“…Recently, Bowden and Hassan [23] used planar (two-component) PIV to study the OGE phenomena in a single downward discharge. Their results demonstrated the ability of the planar PIV to record the liquid-phase velocity field, but they found several technical challenges in adopting the PIV system.…”

“…The similarity relationship was used by Bowden and Hassan [23] to develop a scaled test section which could be used in conjunction with their PIV experiments. The same test section is used in the present study and is shown in Fig.…”